Every home produces moisture from cooking, showering, breathing, and drying clothes. In an older, draughty home, that moisture escapes through gaps in the building fabric. Once you insulate or seal those gaps, it has nowhere to go.

The result is condensation, damp, and mould. Over time, poor air quality builds up too, with higher CO2 levels and stale air that affects sleep, concentration, and health.

Ventilation is not a bolt-on. It is part of the same problem as insulation.

Types of ventilation

The right ventilation approach depends on how airtight your home is and what other improvements you are making. Here is how the main options compare.

Type

Natural ventilation

MEV

MVHR

Impact on heat

High: air and heat escape through gaps

Moderate: fans pull warm air out with the moisture

Low: recovers up to 90% of heat before it leaves

Best suited to

Draughty older homes not yet insulated

Homes with bathroom or kitchen fans already fitted

Well-insulated homes being sealed or significantly upgraded

How it's controlled

None: relies on wind and gaps

Manual or triggered by humidity sensors

Continuous and automatic across the whole house

Control

None: weather-dependent

Manual or humidistat-triggered

Continuous, automatic, whole-house

What to watch out for

Most homes already have some form of extract ventilation, typically a bathroom fan or kitchen extractor. But these are often undersized or poorly installed, which means they are not removing enough moisture to do their job.

Material choice matters too. Breathable materials like wood fibre allow some moisture movement through the wall. Vapour-closed boards like rigid PIR foam do not. Your ventilation strategy needs to account for which approach is used, because getting this wrong can cause the insulation itself to trap moisture inside the wall.

The short version: insulation and ventilation need to be designed together. If they are not, you may fix one problem and create another.

"Extraction fans are often undersized and underperforming, so they are not actually able to take moisture out of your home. This is one of the most common mistakes we see when people insulate without a whole-house plan."

Becky Lane, Founder and CEO at Furbnow

How Furbnow approaches ventilation

Ventilation is assessed as part of every whole-house survey, not treated as an afterthought. Our PAS2035-certified retrofit coordinators measure how well your existing fans perform, identify moisture risks, and model how your proposed insulation will change airflow through the building.

The result is a ventilation strategy designed for your specific home, accounting for the materials being used, the airtightness you are targeting, and the rooms most at risk.

Get it right from day one

If you are planning insulation, draught-proofing, or a heat pump, ventilation should be part of the conversation before work starts, not something you retrofit later. A Furbnow Home Energy Plan designs your ventilation strategy alongside every other improvement, so nothing gets missed and nothing undermines anything else.